Chandra and Magellan/FIRE follow-up observations of PSO167-13: an X-ray weak QSO at $z=6.515$

Abstract

Context. The discovery of hundreds of quasi-stellar objects (QSOs) in the first Gyr of the Universe powered by already grown supermassive black holes (SMBHs) challenges our knowledge of SMBH formation. In particular, investigations of z > 6 QSOs presenting notable properties can provide unique information on the physics of fast SMBH growth in the early universe. Aims. We present the results of follow-up observations of the z = 6.515 radio-quiet QSO PSO167-13, which is interacting with a close companion galaxy. The PSO167-13 system has been recently proposed to host the first heavily obscured X-ray source at high redshift. The goals of these new observations are to confirm the existence of the X-ray source and to investigate the rest-frame UV properties of the QSO. Methods. We observed the PSO167-13 system with Chandra/ACIS-S (177 ks), and obtained new spectroscopic observations (7.2 h) with Magellan/FIRE. Results. No significant X-ray emission is detected from the PSO167-13 system, suggesting that the obscured X-ray source previously tentatively detected was either due to a strong background fluctuation or is highly variable. The upper limit (90% confidence level) on the X-ray emission of PSO167-13 (L 2−10 keV < 8.3 × 10 43 ergs −1 ) is the lowest available for a z > 6 QSO. The ratio between the X-ray and UV luminosity of α ox < −1.95 makes PSO167-13 a strong outlier from the α ox − L UV and L X − L bol relations. In particular, its X-ray emission is > 6 times weaker than the expectation based on its UV luminosity. The new Magellan/FIRE spectrum of PSO167-13 is strongly affected by the unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted. Conclusions. The most plausible explanations for the X-ray weakness of PSO167-13 are intrinsic weakness or small-scale absorption by Compton-thick material. The possible strong blueshift of its emission lines hints at the presence of nuclear winds, which could be related to its X-ray weakness.

Co-evolution of massive black holes and their host galaxies at high redshift: discrepancies from six cosmological simulations and the key role of JWST

“…Since in the following we are interested in the brightest objects formed in the simulations, we do not correct the simulated BH population with a possible obscuration of the BHs. The population of z 6 quasars known to date are mostly non-obscured type I quasars (see discussion in Connor et al 2019;Vito et al 2019;Connor et al 2020;Vito et al 2021). This is likely due to a bias against obscured quasars in the selection process of z > 6 quasars, as observations have identified obscured quasars up to z ∼ 4.6 (e.g., Assef et al 2015;Vito et al 2020;Diaz-Santos et al 2021).…”

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XIV. A Candidate Type-II Quasar at z=6.1292

“…Vito et al (2021) recently reported no significant X-ray emission from Vito et al (2019)'s z = 6.515 source with deeper followup observations with Chandra.…”

Enhanced star formation in $z\sim6$ quasar companions

“…In particular, Venemans et al (2020) followed up with the Atacama Large Millimeter Array (ALMA) a sample of 27 z ∼ 6 quasars, previously detected in [CII], discovering 17 [CII] bright galaxies and finding that some of the quasars present multiple (2-3) companions. Furthermore, whereas no dual AGN has been confirmed so far at z > 6 (Connor et al 2019(Connor et al , 2020Vito et al 2019Vito et al , 2021, several of them have been detected up to z ∼ 5 (see Koss et al 2012;Vignali et al 2018;Silverman et al 2020).…”

“…These conflicting observational results could be explained by the difficulty in detecting the satellites in the neighborhood of a luminous quasar, where the strong AGN feedback can play a fundamental role in shaping their baryonic component. AGN feedback could affect the MBH environment well beyond the host galaxy scale radius and significantly modify the star formation (SF) activity of the orbiting companions (see Martín-Navarro et al 2019, 2021. Dashyan et al (2019) explicitly investigated, in cosmological hydrodynamical simulations, the AGN-driven quenching effect within galactic satellites at low redshift (z < 3).…”